Conventionally, a fluid brake device is known. A fluid brake device carries out variable control of a viscosity of a magneto-rheological fluid (MRF) which is contained within a fluid chamber formed in a container and come in contact with a brake member by controlling magnetic flux passing through the MRF. The fluid brake device can apply braking torque to the brake member by comparatively small electric power. Therefore, the fluid brake device is preferable to a variable valve timing apparatus which adjusts a relative angular phase between a crankshaft and a camshaft according to a braking torque generated by the fluid brake device. The relative angular phase may be called as an engine phase indicating a valve operating timing.
JP 2010-121613A discloses one of the variable valve timing apparatus with the fluid brake device. The device has a case, a brake member disposed in the case, and a brake shaft fixed on the brake member and rotatably supported on the case. The device has a fluid sealing structure fluidly seals between the brake shaft and the case. The device further has a movable member that increases or decreases a capacity of the fluid chamber in accordance with an increase or decrease of pressure within the fluid chamber. In the disclosed fluid brake device, a temperature in the fluid chamber may be increased by thermal energy produced by friction between the MRF and the brake member, etc. The movable member may moves to increase the capacity of the fluid chamber in response to a pressure increase within the fluid chamber caused by a temperature increase. Since a capacity increase of the fluid chamber can decrease a pressure in the fluid chamber, the capacity increase caused by the movable member may reduce a pressure increase within the fluid chamber.